This invention relates to volatile memory elements, and more particularly, to circuitry for clearing memory elements.
Integrated circuits often contain volatile memory elements such as static random-access memory (SRAM) elements. Memory elements can be used to temporarily store data during data processing operations. For example, an integrated circuit that contains processing logic may contain an array of SRAM elements for storing data that is used by the processing logic. Memory elements may also be used in memory chips. Circuits such as field-programmable gate arrays and other programmable devices may contain memory elements that store configuration data for configuring programmable logic.
During operation of an integrated circuit with memory elements, data may be written into the memory elements and may be read from the memory elements. In some situations, it is desirable to clear a group of memory elements. For example, it may be desirable to clear a group of memory elements on a field-programmable gate array before configuration data is loaded into the memory elements. The clearing process ensures that the memory elements have a desired state (i.e., each memory element contains a logic zero). Once cleared, the memory elements may be reliably loaded with desired data.
To facilitate clearing operations, some memory element designs include a dedicated clear transistor in each memory element. The clear transistor may be coupled between a data storage node in the memory element and a ground terminal. When it is desired to clear a memory element of this type, a clear control signal can be asserted. The clear control signal turns on the clear transistor and pulls the data storage node to ground, clearing the memory element. Memory elements can be cleared in this way during power-up operations or after an integrated circuit has been powered.
In conventional memory element designs such as these, a significant amount of circuit resources are devoted to supporting clear operations, because each memory element is provided with a dedicated clear transistor.